Correlation between axial length and refractive error in emmetropic and myopic Iraqi adults

Integrating axial and anterior-segment measures, along with quadratic prediction and odds-based models, can support diagnosis, risk stratification, and management.

The aim of this work is to quantify the axial length (AL) - spherical equivalent (SE) relationship in Iraqi adults, assess sex differences within refractive categories, and develop prediction and risk models.

Cross-sectional study of 2,948 eyes (18-33 years) at a university eye-care clinic (Feb - May 2025). SE was measured by non-cycloplegic autorefraction (Nidek ARK-1) and AL by SS-OCT biometry (ZEISS IOL-Master 700). Refractive groups were emmetropia (-0.50 D < SE ≤ +0.50 D), mild myopia (-0.50 to -3.00 D), and moderate myopia (-3.25 to -6.00 D). Group differences were analysed with t-tests/ANOVA. Sex-stratified, within-category SE was examined with equivalence testing (TOST; ±0.25 D). Ordinary least-squares models predicted AL from SE and SE², and SE from AL and AL², adjusting for age and sex. Logistic regression mapped AL to odds of any myopia versus emmetropia and of moderate versus emmetropia plus mild; discrimination was evaluated by the ROC/AUC.

Mean SE was +0.11 ± 0.29 D in emmetropia and -3.25 ± 1.67 D in myopia; mean AL 23.33 ± 0.60 mm and 26.03 ± 1.17 mm, respectively. AL differed across categories (p < 0.001). Females had longer AL within emmetropia (≈0.57 mm) and within mild - moderate myopia (≈0.70 mm; both p < 0.001), while SE was equivalent by TOST. The AL - SE association was range dependent: strong and negative in emmetropia/mild myopia (R² ≈ 0.83) and weaker in moderate myopia (R² ≈ 0.45). Quadratic models improved prediction (adjusted R² ≈ 0.936 for AL; ≈ 0.934 for SE; RMSE 0.42 mm and 0.54 D). Longer AL significantly increased the odds of myopia after adjustment.

AL closely tracks refractive status with range-dependent coupling. Females show longer AL without SE shifts, implying anterior segment compensation.